Steel heat treatment



Patented Nov. 30, 1943 2,335,506 STEEL HEAT TREATMENT Raymond A. Grange, Jersey City, N. J., assignor to United States Steel Corporation of Delaware,

a corporation of Delaware No Drawing. Application December 5, 1942, Serial No. 467,987

3 Claims. (01. 148-215) the transverse ductility of hot-rolled steel plate and sheet. Obviously only the non-carbonaceous inclusions are of this character, since the carbides are not plastic at steel hot-working temperatures and, therefore, are not worked into plate-like bodies,- or laminations, during hot working involving flattening of the steel.

According to the invention, steel containing such flattened, non-metallic inclusions, is heated to temperatures high enough to render these inclusions mobile, and held, at such temperatures, until the inclusions convert to discontinuspheroidal jj uately high temperatures, the inclusions Qoalesce into areas of discontinuous spheroids if if given adequate time. The exact time and temperature required can be ascertained by heating steel to different temperatures for different times, metallographic examinations serving to show when the temperature and time are adequate to produce the desired effect. When the inclusions assume the form of discontinuous spheroids, they do not affect the propertiesotsteel so adversely as they do when in their flattened form.

As a specific example of the invention, S. A. E. X4130 sheet steel, which had been worked, to a .105" thickness, so as to include suflicient hotrolling to produce the relatively thin, flattened plates of non-metallic inclusions, prevalent in this particular steel, was heat treated in accordance with this invention, by being soaked at temperatures within the range of fromyabout 1900 to 2300 F. for about 20 hours, while sealed in an air-tight enclosure to protect it from oxidation and decarburization, subsequent metallographic examination showing that the specified form. In other words, at adenature of hot-working The described treatment results in a new product, namely, hot-worked, elongatedsteel, of any type, containing non-metallic inclusions that are plastic at the steels hot-working temperature and which are in discontinuous, spheroidal form, as contrastedto the continuous, flattened plates of such inclusions, common to the prior art steels.

During the heat treatment, it is usually desirable to protect the steel against oxidation and, in some instances, 'decarburization. It is to be understood that the described heat treatment should usually be applied after all hot-working has been finished, because further hot-working might again flatten the inclusions. At the same time, the treatment may be applied just prior to the last stages of hot-rolling, if the latter does not flatten the steel too much. As previously mentioned, the invention is applicable to any type of steel containing inclusions that are plastic at the steels hot-working temperatures, and which are flattened by hot-working of the steelso as to adversely afiect the steels properties. It is also applicable to products whose results in elongated, continuous stringers of such inclusions, such as are produced in hot-rolled round shapes, if it is considered, for any reason, that such stringers are more harmful than discontinuous strings of 0 spheroids.

I claim:

1. A method of treating steel containing elongated non-metallic, non-carbonaceous inclusions that are plastic at the hot-working temperature of the steel, comprising heating the steel to temperatures high enough to render such inclusions mobile and holding at said temperatures until said inclusions convert to discontinuous spheroidal form.

2. A method of treating steel containing elongated non-metallic, non-carbonaceous inclusions that are plastic at the hot-working temperature of the steel, comprising heating the steel totemperatures of from about 1900 to 2300 F.

5 for a period suflicient to effect an appreciable inclusions had been largely converted into discontinuous spheroids. Comparative bend tests 01' this steel, before and after this heat treatment, showed material improvement in its transverse ductility.

degree of coalescence of the inclusions.

3. Hot-worked, non-metallic, non-carbonaceous inclusions that are plastic at the steels hot-working temperature and which are in discontinuous spheroidal form.

RAYMOND A. GRANGE.

elongated steel containing 

